An image forming apparatus including a thermostat arranged in a housing of a fixing device with terminals on both ends arranged slanted with respect to a longitudinal direction. A non-contact type temperature sensor is arranged adjacent to the thermostat. Discharge rollers are arranged at equidistance from a center reference line according to a smallest width of paper on a downstream side in a conveying direction of the paper of a housing. A center part of the thermostat and an opening for temperature detection of the temperature sensor are positioned between the discharge rollers.